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| -rw-r--r-- | doc/dev/osd_internals/pg.rst | 31 |
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diff --git a/doc/dev/osd_internals/pg.rst b/doc/dev/osd_internals/pg.rst new file mode 100644 index 000000000..397d4ab5d --- /dev/null +++ b/doc/dev/osd_internals/pg.rst @@ -0,0 +1,31 @@ +==== +PG +==== + +Concepts +-------- + +*Peering Interval* + See PG::start_peering_interval. + See PG::acting_up_affected + See PG::PeeringState::Reset + + A peering interval is a maximal set of contiguous map epochs in which the + up and acting sets did not change. PG::PeeringMachine represents a + transition from one interval to another as passing through + PeeringState::Reset. On PG::PeeringState::AdvMap PG::acting_up_affected can + cause the pg to transition to Reset. + + +Peering Details and Gotchas +--------------------------- +For an overview of peering, see `Peering <../../peering>`_. + + * PG::flushed defaults to false and is set to false in + PG::start_peering_interval. Upon transitioning to PG::PeeringState::Started + we send a transaction through the pg op sequencer which, upon complete, + sends a FlushedEvt which sets flushed to true. The primary cannot go + active until this happens (See PG::PeeringState::WaitFlushedPeering). + Replicas can go active but cannot serve ops (writes or reads). + This is necessary because we cannot read our ondisk state until unstable + transactions from the previous interval have cleared. |